Abstract

This paper describes a 4-step approach to the identification and modelling of those 'land-units' that regulate the water, ion or particulate fluxes observed at the catchment scale. The steps are illustrated with examples of water, nitrate, and particulate fluxes within the Slapton Wood Catchment (Devon) and the Baru Catchment (Malaysian Borneo). These steps are: (1) Identify 'spatial patterns' (or variability) of flux integrated over 'large land-units' (i.e., 10 ha, or at least 1 ha in plan area) of a catchment. A nested contributory area structure can be used. (2) Identify and then focus on the locally important / dominant patches (land-units). (3) Characterise the 'temporal patterns' (dynamics) of representative land-units (in particular those with a high water, ion or particulate flux) given dynamic input variables (e.g., rainfall). An approach not constrained by physical concepts, that may be inappropriate at the 10 ha scale, may be a useful starting point (e.g., Data-Based-Mechanistic modelling). (4) Correlate flux patterns with those of 'catchment parameters', both observed at hectare-scales. Physical concepts / theory need to be addressed to understand which catchment parameters (e.g., permeability) are correlated with the flux patterns, however, this may require new parameter measurement directly at the scale of the 1-10 ha land-unit.